Electric current integrating apparatus



Sep 11, 1951 R. H. DICKE 2,567,276

ELECTRIC CURRENT INTEGRATING APPARATUS Filed Dec. 26, 1947 2 Sheets-Sheet 1 Fla-.1; 61

voltmeter A lifier FIG-.2.

FIG.3. 5 {ii-LT?) 1 v Amplifier mmvrm ROBEPTHDICKE yaw/(W HIS ATTORNEY Sept. 11, 1951 R. H. DICKE ELECTRIC CURRENT INTEGRATING APPARATUS 2 Sheets-Sheet 2 Filed Dec. 26, 1947 0n v vm El w INVENTOR. ROBERT H. 131cm:

ms ATTOQNEY most sensitive, instrument.

a ballistic galvanometer is used only in the Fig. 4 construction.

Peteiited Sept. 11,1951

STATES PATENT OFFICE auzc'rn c CURRENT INTEGRATING APPARATUS Robert H'. Dicke, Princeton, N. J. Application December 26, 1947, Serial No. 794,027

9 Claims. (o 171-95) -"invention relates to variable current 'andZor var iable voltage, pulse or surge integratir'ig" meters and more particularly to a meter of thisikind which is extremely sensitive and accurate'fand' which lends itself to a multiplicity of scale readings to afford measurements over a large' irange of values.

In'order to measure the quantity of current ilow"'d'ue to a? variable temporarily existing voltageor current-flow, which follows no particular law of variation; it is necessary to integrate the successive increments of the current flow. One exampleofsuch a problem presents itself when the'present invention to construct the apparatus by the inclusion of electronic amplifiers in a manner such that the amplifying ratios of the electronic tubes is not a factor entering into g the accuracy of the apparatus and may even during the period of current or voltage ,-integration.

- Another object of the present invention resides in the construction of the apparatus so that the same apparatus may be used for both voltage and currentinte gration.

A Gras'sot meter differs from a ballistic galvanometerlboth of which may be used. in that a low-return period is obtained in a ballistic galvanometer by increasing the inertia of the moving element whereas in the Grassot instrument thls low period is obtained by decreasing the returning "torque. "];The latter is therefore the A Grassot meter or Anoth'enobiectof the invention resides in the provj'lsion of means to enable'the reading of the capacity of a" condenser if the voltage of a charge theredn is known.

Another object of the invention resides in the proyisionoif a e rch coil the dimensions of which andnumber of of which is known to be used with thejapparatusso as to enable flux density or total duties the case may be, of a magnetic iicld'to be measured.

Another object resides in the provision of means to enable the inductance of an inductive reactor to be read, if the direct current originally applied thereto is known.

Another object of the invention resides in the provision of numerous adjustments to change constants of the apparatus in order to provide numerous scale calibrations each characterizing a different degree of sensitivity of the apparatus.

Another object of the invention resides in the construction of the apparatus so that practically noenergy from the source to be integrated is consumed by the apparatus. This enables a search coil having many turns of fine wire to be used so that-magnetic field strength of almost zero intensity can be measured and it also enables the capacity of extremely small condensers to be measured. i

Another object of the present invention resides in the provision of a shunt whereby a potential integrating apparatus may be used for integrating current pulses. I

Another object of the invention resides in the construction of the apparatus so that its accuracy, even when integrating extremely small voltages or currents, depends only on the accuracy of the voltmeter or milliammeter used with the apparatus and the constants of precision components of resistance and capacity used, all of which are available on the market. Although a galvanometer and an amplifier are used as elements of the particular embodiments of the invention disclosed, neither the accuracy of the galvanometer nor the stability of the amplifying factors of the amplifying tubes used as elements of the apparatus impair the accuracy of the resulting readings.

Other objects, purposes and characteristic fea- I tures of the invention will in part be pointed out hereinafter and will in part be obvious from the accompanying drawings of which:

Fig. 1 shows conventionally one embodiment of the invention;

Figs. 1A, 1B, and 1C illustrate a different turn search coil, an ampere shunt, and a capacity test adapter respectively;

Figs. 2, 3, and 4 illustrate three other forms the present invention may take and of which Fig. 2 constitutes a current integrating device; and

Fig. 5 illustrates in more detail the embodiment of the invention illustrated in Fig. 1 together with means for'electrically adjusting the drift so as to cause the instrument to normally assume the zero, indicating position.

Structure Fig. 1.By referring to Fig. 1 it will be seen that a search coil S01 has by its plugs l I been illustrated plugged into the two receptacle sockets I2 of the integrating apparatus. This apparatus includes a galvanometer G1 including a permanent magnet PM ior producing a strong magnetic field in which a coil I4 is preferably suspended by a suspension ribbon. This coil it supports a mirror M which projects a beam of light from the lamp Lti upon the two cathodes C01 and Co: of two single or one double photoelectric tube PETi. This galvanometer movable coil I4 is supported so as to surround the stationary core or cylinder 9 of magnetic material, this stationary core being used to reduce the reluctance of the permanent magnet produced magnetic field and to thereby produce a strong magnetic field in the airgap in which the coil l4 moves. The core 8 as shown is supported by the upper pole shoe by suitable non-magnetic material such as brass or insulation It. The circuit through the search coil $01 includes the coil ll of the galvanometer and the precision resistance R1. The plate P2 of the photo-electric tube PET1 is connected to the cathode Ca; so that this junction point constitutes an intermediate point in the potential gradient through this tube and a wire i leads from this point to the amplifier grid (see Fig. 5). The other two wires 16 and 11 leading from plate P1 and cathode Caz, respectively, of tube PETi areconnected to the positive and negative terminal, respectively, of a plate source of current. The output leads l8 and I! of the amplifier A1 are connected to a circuit including the condenser C1 and the resistance R1 in series,. a voltmeter Vm being connected across the output leads l8 and IQ of the amplifier A1. In practice the light beam from lamp Lti reflected from the mirror M strikes the two cathodes C111 and Car of photo-electric tube PETi in a manner such that zero potential exists across the voltmeter Vm. This may be accomplished by drift adjusting means such as disclosed in Fig. 5 and described hereinafter or, if desired, the galvanometer G1 may be adjusted mechanically by adjusting its return suspension spring to produce such result. The galvanometer G1 is preferably very sensitive and has an extremely low centering torque but need not have any particular graduation or number of turns on its coil l4.

Operation Fig. 1.Let us assume that the proper mechanical or electrical drift adjustment has been made in the Fig. 1 structure to cause the voltmeter Vm to indicate zero. Let us now assume that the search 0011 S01 is moved at any speed either fixed or variable but preferably at a low speed, into a magnetic field. This will cause varying voltages to be induced into search coil SCi in accordance with the varying rate at which magnetic lines entering the coil have been cut. These voltages cause slight movement of the coil I of the galvanometer G1 as a result of which the light beam 13 is deflected and the amplifier A1 is controlled to cause this amplifier to produce feed back current flow through condenser C1 and resistance R1 to cause the resistance R1 to develop a voltage drop or counter voltage which substantially equals but is in an opposite direction to the voltage induced originally into the search cell 801. This will cause current flow into the condenser 01 at each instant proportional to the voltage then existing at the terminals of the search coil SC and therefore the condenser Ci constitutes the accumulator reservoir of an electrical integrating device. When the voltage induced in search coil SC1 falls to zero, as it will when the magnetic lines to be measured have all penetrated the search coil, the voltmeter Vm may be read to read the potential to which the condenser C1 has been charged.

The condenser remains charged for a considerable period, possibly 20 minutes, because the amplifier A1 continues to maintain a potential across its output leads in a direction to hold this charge. No current however fiows through resistance R1 or search coil S01 due to this potential. This function is accomplished in this way. If a very minute current flows from condenser C1 in a discharging direction this current fiows more readily through the galvanometer and search coil than through resistance R1. This current fiows, and to a very slight extent only. through galvanometer G1 in the same direction it originally flowed due to magnetic lines entering the search coil SC for reasons presently pointed out. This current will therefore act through galvanometer G1 and photo-electric tube PET! to cause the amplifier A1. to hold its plate potential applied to voltmeter Vm substantially where it was when voltage ceased to be induced in search coil SC1. This process of having the amplifier suppress discharging of the condenser C1 and at the same time supply the additional current which flows through the voltmeter Vm enables a very accurate reading to be obtained in that ample time for allowing the voltmeter pointer to come to rest is afforded. It is thus seen that current flows from the amplifier A1 and into the condenser C1 during each increment of time that potential is induced into the search coil and of a value commensurate to such potential, because the voltage drop caused by this current flowing over R1 is substantially exactly equal to and opp site to that of the voltage induced in the search coil SC1 and the charge in the condenser C1 is therefore an indication of the voltage integration, that is, is a product of each increment of voltage and the time such voltage existed. and this is proportional to the total number of magnetic lines that entered or left, as the case may be, the search coil 861. The fact that the energy for charging the condenser is supplied by the amplifier A1 and not by the search coil renders the apparatus extremely accurate, based of course on the assumption that the voltmeter Vm is accurate and that the precision resistor R1 and precision condenser C1 are of good quality and have constant known values. By looking at the movable element of the galvanometer through a jewelers magnifying glass when the apparatus was in use no movement of this element or coil I4 could be observed. This is due to the fact that as soon as galvanometer coil H and mirror M move to an unnoticeable extent an output current is produced by the amplifier A1 which flows in a direction through resistance R1 to result in a countervoltage which is almost exactly equal to and opposes the voltage induced in search coils S01 and to thereby prevent further movement of the coil H. The current flowing in the output circuit of the amplifier A1 is therefore ,at all times substantially proportional to the potential induced in this search coil. It should be understood that search coils of various diameters, shapes, and number of turns (see Fig. 1A) may be used with the instrument or apparatus of Fig. 1 and that dial switches for inserting various precision condensers and precision resistances, as shown in Fig. 5, may be employed in the Fig. l construction. In order to accelerate the discharging of the. condenser 01 a shunting contact or push button PB .such as shown in Fig. may be provided.

Structure. Fia. 2.--The form on invention ll lustrated in Fig. 2 is particularly\ designed ior current integration. In this connection it should be understood that the Fig. 1 construction may be used for current integration ii the current to be integrated is allowed to flow through the shunt SH illustrated in Fig. 13 to thereby convert current fiow into corresponding potential drop. In the Fig. 2 structure the galvanometer G: is included in the circuit the current of which is to be integrated but only an insignificant portion of this current actually flows through the galvanometer because the amplifier A: produces the equivalent of a current sucking effect to an extent that substantially all of the current pulse through the circuit, and to be integrated, passes through condenser C4 and amplifier A: and builds up an integrating charge in this condenser. -Except for the difference that the condenser C4 is connected directly to the receptacle #2 and the resistance unit R1 of Fig. l is replaced by a low resistance wire, the Fig. 2 construction is identical to the Fig. 1 construction, and therefore like parts have been designated by like reference characters having distinctive suillxes.

Operation Fig. 2.-To use the apparatus illustrated in Fig. 2 the circuit in which the current pulse to be integrated fiows is opened and the two wires formed by such opening are plugged into the two receptacles i2 oi Fig, 2. It is assumed that drift was adiusted to a point where the voltmeter Vim indicates zero before hand. its the current pulse to be integrated tries to pass through galvanometer G: the light beam II is so quickly deflected and the amplifier A: so quickly produces a voltage of the proper polarity to cause substantially all the current of the current pulse to be measured to pass through condenser C4. This causes a charge to be built up in the condenser C4 commensurate with the current integration. This charge is of course read on the voltmeter Vm the same as in the Fig. 1 construction. The voltmeter Vm will remain in its indicating position for a long time because the tendency for the condenser to discharge through the galvanometer G: produces a voltage in the output circuit 01' the amplifier A: of a polarity as did the original current so thatthe condenser C4 is discharged extremely slowly. The capacity of the condenser shown in Fig. may, for instance, be measured by using the ap- -paratus shown in this Figure 10 with the apparatus shown in Fig. 2. To measure the capacity of any condenser, such as condenser C; for instance, the plugs 2| of Fig. 1C are plugged into the receptacles i2 01' Fig. 2 and the switch is placed in its left hand position until the condenser C; has been charged to a particular voltage presumably the voltage of battery 2'. The switch 25 is then thrown to the right and alter the voltmeter Vm of Fig. 2 has reached a stable indication position the voltage is read. By these two voltage readings and the capacity oi! the condenser 04 which is known. the capacity of condenser C: may be determined by the algebraic expression where Vb represents the voltage oi battery 26.

What has been said in regard to determining once unit by allowing current from an inductive kick to pass through the apparatus of Fig. 2.

Structure Fig. 3.In the Fig. 3 construction the accumulator or integrator comprises an inductive reactor L1 and an ammeter Am which is used to indicate the strength oi the magnetic field that has been built up and stored in inductive reactor L1. That is. the measure of the potential energy that is stored in the magnetic field o! the inductive reactor L1 is indicated by the strength of the magnetic field as maniiested by the current iiow through such reactor 'to build it up. It will be seen that the reactor Li and ammeter Am are included in series across the output terminals il-IQ oi the amplifier A3. The Fig. 3 construction like that of Figs. 1 and 4 is a potential integrating apparatus in that the current eventually built up in the inductive reactor L1 is proportional to the sum of the increments of voltages (counter E. NL'F.) appearing across the reactor during the building up of such field. The galvanometer G: is included in series with the inductive reactor Li and since the galvanometer, photo-electric and amplifier structure is such as to hold the galvanometer current substantially at zero the counter E. M. F. induced in reactor L1, by current principally derived from the amplifier, is substantially equal to the voltage increments appearing across receptacles I2 01' Fig. 3. These voltage increments might,. ior instance, be the falling voltage appearing across the condenser 03 as it is dising increase in current flowing through thischarged through a resistance, Rs 01' Fig. 1B.

Operation Fig. 3.Ii one of the search coils 801 or SC: is plugged into receptacles i2 01 Fig. 3 and this search coil is moved so that the magnetic field to be measured is suddenly, or at any medium constant or variable speed. cut by all of the turns 0! the search coil a voltage appears across the terminals of the search coil varying with the-rate of cutting of magnetic lines by the conductors'ot the search coil. Each increment of this voltage results in a corresponding increment of voltage being applied across the reactor L by the output leads i8 and is of the amplifier A2. Since each increment of voltage present across the reactor Li causes a correspondreactor, the total current flowing through reactor Li which may be read on the ammeter A171 is a measure of the sum of the increments oi voltages induced in search coil SCi or 8G2, and is a measure of the total magnetic flux linking the search coil. It now the inductive reactor L1 is fully discharged by closing, for a moment only. the reset switch 25 and the search coil is then removed from the magnetic field to be measured the same reading, namely a check reading, will be given except that the ammeter will read backwards, it being assumed that an ammeter is used having its rero reading at an intermediate point on the scale.

Structure Fig. 4.-The Fig. 4 construction is identical to the Figs. 1 and 5 construction except that the condenser C; has been replaced by the ballistic galvanometer BG. ThLs ballistic galvanometer is calibrated in coulombs 'for which reason the voltmeter Vm is no longer a necessary element of the system and has been omitted from the drawing, although it may retained without impairing the accuracy of the apparatus. A ballistic galvanometer is an instrument having? a relatively heavy moving element as conventionally illustrated by the flywheel or mass W and is is biased to a zero position by a suspension balance siderable period of time.

having an extremely long period such that it willnot be diificult to read the mazrlmuurswingof the needle. By this slow period characteristic it will be capable of integrating voltage over a con- Although the suspension structure of the galvanometers G1, Ga, Ga, G4 and BG have not been specifically illustrated it should be understood that preferably an upper and a lower suspension conducting tape is employed in each instrument and that these tapes are insulated from each other and that one tape is used to conduct current into the-dynamometer coil whereas the other tape conducts the current from the coil. By reason of the slow period or the galvanometer BG its coil 26 will not have materially changed its position by the end of the period during which voltage integration takes place. The coil and pointer keep on moving however for reasons given below. The amplifier produced current, variable in practice, causes kinetic energy to be built up in the flywheel or core wheel which is proportional to the current integration and this current at each instant is proportional to the voltage impressed across receptacles i2 of Fig. Q by' the search coil. This kinetic energy produces an arc of swing of the needle 21 against the bias of the tortlonal suspension spring proportional to this kinetic energy that is, converts it into potential energy, by ilexin the spring, so that the scale of the galvanometerBG may be, and in practice is. calibrated in coulombs, and by using the proper multiplying constant, as determined from resistance of unit R4 and the number of turns in coil SCi. may be read in magnetic lines or Gauss.

Instead of using a ballistic galvanometer as shown in Fig. 4 a so-called G'rassot meter may be used to perform the integrating function. This Grassot meter when used is connected the same as is the ballistic galvanometer B6 in Fig. 4,

and has all the attributes of the ballistic galvan ometer and has the additional ballistic attribute of having a smaller mass and a correspondingly lighter suspension balance and furthermore is strongly damped by its winding which moves in a very stron magnetic field. For convenience, these two instruments both of which have variable surge or pulse integrating abilit will be called :dynamic energy storing and indicating means."

portional to the average strength of an electrical surge times the time duration of such surge, that is, an-arc of swing proportional to the sum of the increments of such surge.

Operation Fig. 4.--Let us assume that the search coil S01 or SC: (Figs. 1 and 1A) is inserted in the receptacles I! of Fig. 4 and that the search coil is moved into the magnetic field the strength of which is to be measured. This will ,of course cause the induction of a voltage in the search coil at all times proportional to the rate at which magnetic flux enters the turns of the coil which may vary and may continue for an unknown but short period of time. Through the medium of galvanometer G4, photoelectric tube PET4, and amplifier A4 and for reasons heretofore given, the amplifier causes a current to flow through resist-- ance R4 which is at all times proportional to this induced potential in coil $01 or SCn and which is at each instant of value to produce a resistance current drop which is substantially equal to and opposite to the induced voltage.

in glass W which ls'proportional to the sum of Each of these instruments will pro- 7 duce an arc of swing of its moving element pro- This current, which in practice varies, builds up kinetic energy the increments of this current to thereby, pro

duce a maximum swing of needle 21 (potential Structure and operation Fig. 1B.---The shunt, SH illustrated in Fig. 13 may be used with any one of the apparatuses illustrated in Figs. 1, 3, 4. and 5 in the same way as any ammetershunt may be used with a low reading voltmeter or millivoltmeter in order to read amperes on such voltmeter, that is, this shunt may be used with the voltage integrating structures disclosed in order to integrate increments of current. words the apparatus illustrated in Figs. 1. 3, 4 and 5 are voltage increment integrators or voltage-' time integrators. and by use of shunt SH (Fig. 13) current may be converted into volts through the medium of the ohmic resistance of the shunt SH. In using the shunt of Fig. 13 either the search coil SCr or the search coil SC: or the circuit the current which is to be integrated may be plugged into the receptacles 29 (Fig. 1B) and the plugs 20 may then be plugged into the receptacles i2 of Figs. 1, 3, 4 or 5 and in so doing increments of current may be integrated by apparatuses built for the purpose of integrating increments of voltage.

Structure Fig. 5.-,In Fig. 5 has been illustratedin somewhat more elaborated form the apparatus illustrated in Fig. 1. That is, substitute resistances R2 and R3 which may be substituted ior resistance R1, and a condenser C2 which may be substituted for condenser C1 have been provided and illustrated. Also, an electrical drift adjuster including an adjustable potentiometer P0 has' been added and the amplifier A1 including amplifying tubes Tl, T2 and T3 has been shown in more detail. Also, a zero set including a push button switch PB and a discharge resistance R30 have been added. It should be understood that similar substitute condensers, resistors and inductive reactors are presumed present in the structures of Figs. 2, 3 and 4, and that the amplifiers A2, A; and A4 are identical to-amplifier A1 of Fig. 5 and that they include similar drift adjusting potentiometers. As already stated the galvanometer G1 includes a mirror M mounted on the moving coil H supported by a suspension pivot which has extremely low friction. By reason of this substantially frictionless bearing a very substantial deflection in response to substantially zero current flow is accomplished. The continually illuminated lamp Ltl, together with suitable light concentrating means, such as a lens (not shown), a pencil of light from lamp Lti falls on mirror M and is reflected to throw a pencil of light so as to fall to substantially equal extents on the two cathodes Car and Caz oi the double photo-electric tube PETi. electron emission by the two cathodes Cal and Ca: as a result of which the cathode Cal and plate P2, which are connected together, lie potentially substantially midway between the potential of cathode Caz and plate P1. The control grid of the amplifier tube T1 is connected directly to the junction oint 01' elements Cal and P: by

In other This causes substantially equal,

9 wire IS. The flow of current through galvanometer G1 causes the light beam l3 to swing from one cathode to the other of the tube PET1 to thereby cause the potential applied to grid of tube T1 to move up or down and to thereby cause the current flow from plate to cathode of tube T1 to increase or decrease respectively. In practice the plate current in tube T1 usually will rise to thereby cause the potential on the grid oi. amplifier tube T2 to fall by reason of the potential drop through plate resistor R5. Series resistances Re and R7 are used to serve as a potentiometer to reduce the voltage applied to the grid of tube T2 below that'of the plate of tube T1. The reduction of the potential on the grid of tube T2 due to movement of galvanometer G1 in a particular direction causes the plate current from the plate to the cathode of tube T2 to fall to thereby increase the potential existing on the plate of tube T2; Since the grid of tube Ta is directly connected to the plate of tube T11 the potential on the grid of tube Ta is increased to thereby cause an increase in the current flow from the plate to the cathode of tube T3. The cathode of the tube T3 normally stands at substantially the same potential as does the grounded mid-point 35 of the potentiometer P and since this point is grounded, as shown, practically zero potential is normally applied to the voltmeter Vm. In fact by adjusting the contactor 36 of the potentiometer P0 to the proper point on resistor R the proper current will flow normally through resistance Re to cause the cathode of tube T3 to be at the same potential above the negative wire 31 as the point 35 of potentiometer P0 is above this negative wire 31. In other words, the cathode of tube T3 is normally held at ground potential. Since the voltmeter Vm is connected between the cathode of tube Ta and ground no potential normally exists across the voltmeter Vm. Coming back to the point in the discussion where the current flow throu h tube T: was increased, this increase in current flow through the tube T3 causes the potential on cathode oi. tube T3 to rise above that of ground potential, by reason of the counter voltage built up in resistance Ra, as a result of which current is caused to flow over wire I 8, resistance R14, switch 41 and condenser C1, resistance R1, switch 38, wires 39 and ii! to ground and then over resistances R12 and R13 to the terminal minus of plate battery. The flow of current in this circuit portion causes a potential to develop in resistance R1 which holds the current flow in galvanometer G1 substantially at zero. In other words, current is caused to flow to condenser C1 at a rate dependent on the voltage induced in search coil S01 but the actual energy for causing such flow of current is not derived from the search coil but is derived from the amplifier A1. The amplifier is in fact degeneratingly connected so that it feeds back just enough energy to hold the current flowing through galvanometer G1 substantially at zero. When the potential induced in search coil SC1 is of the opposite polarity from that just considered the direction of current flow through condenser C1 is reversed. A wire 401 extends from the junction point between condenser C1 and resistance R1 to the movable contact 38 of the potentiometer P0. This potentiometer includes resistance units R9, R10, R11, R12 and R13. The condenser C5, bridging the resistance R14, is of very low capacity and is used only to prevent a high frequency feed back to be set up in the amplifier which might impair its efllciency although it would not materially interfere with the accuracy of the apparatus.

Operation Fig. 5.-Let us' assume that the search coil S01 is connected to receptacles I2 01 Fig. 5. II the voltmeter is not in its zero indicating position it. should be brought to zero. It may be that the condenser C1 has not been entirely discharged. The condenser C1 may be discharged by momentarily depressing the push button- PB to allow dissipation of the energy stored therein through the resistance R30. At

times even though the condenser C1 was origlnally entirely discharged the voltmeter Vm will still not read zero. This condition may be due to what is conveniently called drift. This lack of constancy of zero reading due to drift may be corrected by adjusting the position of contact 36 on the potentiometer P0. This adjustment of the adjustable contact 36 will cause a small current to flow through galvanometer G1 in a direction to cause the amplifier to function to bring the cathode of tube T1 to ground potential. As already stated drift may also be adjusted to zero by adjusting the spring of the galvanometer G1 and in turn the mirror M. If now the search coil .rent is drawn from search coil SC1 but at the same time a second current flows through condenser C1 which second current at each instant is proportional to the potential existing in search coil 501. When the potential induced in search coil SC1 falls to zero, because all magnetic lines have entered the coil SC1, the current flowing to condenser C1 also falls to zero. The potential existing across this condenser C1 and voltmeter Vm is however not zero because the charge on condenser C1 is still there and this charge is held there by the amplifier A1 and i an indication of the integrated potentials which due to magnetic flux cutting were induced in search coil S01 and is therefore also an indication of the total amount of magnetic flux which entered the coil. The party makin the test may read the voltmeter as soon as its pointer comes to rest and this voltmeter reading is an indication of the magnitude of the flux field or magnetic density depending on the area of the search coil, as more fully pointed out hereinafter. It will take a long time for the condenser C1 to become discharged because each increment of discharge of the condenser C1 through the coil of the galvanometer G1 and the search coil in series and in multiple with resistance R1 produces an efiect upon the amplifier A1 which results in the supply of a voltage on the output leads of the amplifier to prevent such discharge and at the same time supplies the voltmeter Vm. with the current necessary to produce its indication. Ifthe condenser C1 is allowed to discharge in this way it will take from 20 to 30 minutes before it will be completely discharged. Ample opportunity is theresesame reading has been taken. If desiredthe search coil may be removed from the magnetic field as soon as the readin has been taken. If this is done a second reading may be taken due to cutting oi the magnetic lines of flux in the opposite direction. If this is done immediately, without first discharging the condenser. the voltmeter will return to zero, which will be a check upon the first reading taken.

In case the magnetic field to be measured is rather weak a smaller condenser C: may replace the condenser Cl, as by the operation of selecting switch ll. The apparatus illustrated in Fig. 5, by proper selection of the voltmeter scale, condenser size (C1 or'Cz) resistance values (R1, R1 or R3) and search coil turns (SCi or 8C2) may read magnetic field strengths from that emitted by a very small sewing needle to that emitted by a large generator field pole to the same accuracy, in percent. The earths magnetic field may be accurately measured by a search coil having only one square centimeter of cross-sectional area. By use of a larger coil a more accurate reading may be obtained. Since practically zero current flows in the search coil SC during the measurement of magnetic field strength practically zero demagnetizing effect is produced as a result of which more accurate results and readings will be obtained.

It is of course necessary in building the amplifier A1 shown in Fig. to make every efiort to prevent undesirable, either high frequency or low frequency, feed back. The resistance R14 and condenser C5 have been included for this purpose.

In order to give abetter understanding as to how the various embodiments of the invention, when employingvarious precision constants of capacity, resistance and inductive reactance, may be used to make various measurements, let us assume that the following symbol representations are used:

V=voltage at input terminals.

Vb= voltage of battery 28 (Fig. 1C)

vm=vo1tage read on voltmeter Vm.

I=amperes in input circuit.

Im=amperes read on ammeter Im.

t=time in seconds.

Ri=resistance of unit R1 in ohms.

Rs= resistance of unit Rs in ohms.

C1=capacity of condenser C1 in microiarads.

Ca=capacity of condenser Ca in microfarads.

C4=capacity of condenser C4 in microfarads.

H=magnetic flux intensity in gauss.

A=area of search coil in square centimeters.

n=number of turns of wire in search coil.

M=HA=total magnetic flux in maxwells.

Li=inductance of coil LI. in henries.

Qb =reading on ballistic galvanometer in coulom'bs.

1 =charge in coulombs.

i and V=average value 01' current and voltage respectively.

Then the following relationships exist: Fig. 1 (without search coil) 12 Fig. 1 (with search coil) Figs. 2 and 1C:

Fig. 3:

Figs. 3 and 1A:

Fig. 4 (assuming ballistic galvanometer is callbrated in coulombs) Figs. 4 and 1A2 4 bl Idt Rs I Rat R4 OBIR4 I Rst Fig. 5Operation: Same as Fig. 1.

Rsum.-In all forms of the invention the same principle for obtaining efllciency in the integration of voltage or current and the measurement of field strength, capacity or induction is used. This principle resides in the provision of electronic means for supplying current to the Figs. 4 and 1B:

7; measuring instrument at the same rate as the acemvo device whose characteristics are to be measured tends to supply current. In this way the devices upon which measurements are to be taken need supply only an infinitesimal amount of energy to the measuring instrument. This not only renders the apparatus-more accurate but also the magnetic field, for instance, to be measured is maintained in its initial state. That is, substantially no demagnetizing efifect is present. The apparatus of the present invention by reason of the above mentioned features of construction is rendered extremely slow beat as much as 20. to 30 minutes being required to allow the apparatus to restore itself to normal. It is generally understood that an integrating instrument of the type here under consideration has accuracy substantially in accordance with the slowness of its operating beat. Another. feature of the present invention resides in the flexibility of the instrument. For instance, voltmeters and ammeters of various ranges may be used with the same integrating apparatus, and in this integrating apparatus condensers of various sizes and resistance units having various ohmic reenter into the accuracy of the instrument. An-

other way of stating the functioning of the apparatus of Figs. 1 and 5 is that a condenser is charged at a rate depending on a pulse of varying potential independently of its own counterelectro-motive force, so that the amplifier performs more than an amplifying function. That is, the amplifier produces current dependent on an external voltage and independently of the impedance of the circuit through which such current must fiow.

Having thus shown anddescribed several embodiments of the invention and having pointed out how the invention may be used, it should be understood that the disclosures illustrated are merely illustrative of forms the invention may take and does not exhaust all possible combinationsthat may be used and that various changes,

modifications and additions may be made in practicing the invention without departing from the spirit and scope of the invention so long as these changes come within the scope of the following claims.

What I claim is:

1. Varying electric surge integrating apparatus comprising, a condenser, an amplifier supplying current to a circuit including said condenser, electro-responsive means connected to be con.- trolled by said varying surge to be integrated and controlling said amplifier to cause it to generate a second surge fiowing through said condenser which is at each instant substantially equal and oppomte to said varying electric surge to be integrated, said circuit also being connected to said electro-responsive means to substantially neutralize the efi'ect of said surge to be integrated upon said electro-responsive means. and means for measuring the charge on said condenser, whereby the electric energy for charging said charge on said condenser is a measure of the integrated value of said surge to be integrated.

'2. Varying electric surge integrating apparatus comprising, a source of light, a photo-electric tube, a galvanometer connected to be controlled by the electric surge to be integrated and provided with a mirror for directing light emitted from said source upon said photo-electric tube to an extent dependent on the extent of operation of said galvanometer, an amplifier controlled by said photo-electric tube for supplying an electrical energy surge in its output circuit which tends to cause said galvanometer to be returned to its normal position, a condenser in the output circuit of said amplifier for integrating the electrical energy surge supplied by said amplifier, and means for measuring the charge on' said condenser.

3. Varying electric surge integrating apparatus comprising, a source oflight, a photo-electric tube, a galvanometer connected to b controlled by the electric surge to be integrated and provided with a mirror for directing light emitted from said source uponsaid photo-electric tube to an-extent dependent on the extent of operation of said galvanometer, an amplifier controlled by said photo-electric tube for supplying an electrical energy surge in its output circuit which tends to cause said galvanometer to be returned to its'normal position, a condenser included in the output circuit of said amplifier, and means for measuring the charge stored in said condenser.

4. Varying electrical surge integrating apparatus comprising; a source of light; a photo-electric tube; a galvanometer having a permanent magnet, a movable element consisting of a coil in the field of said permanent magnet and a mirror for swinging a light beam from said light source upon said photo-electric tube to an extent dependent on the extent of movement of said element; means for inducing in said coil the electrical surge to be integrated; an amplifier controlled by said photo-electric tube and having its output circuit connected to said coil in such a manner that slight movement of said element due to the surge to be integrated will cause said light beam to swing in a direction to cause said amplifier to act upon said coil so as to return it substantially to its original position; a condenser included in said output circuit; and a volt-meter for measuring the charge on said condenser.

5. Varying electrical surge integrating apparatus comprising; a source of light; a photoelectric tube; a galvanometer having a permanent magnet, a movable element consisting of a coil in the field of said permanent magnet and a mirror for swinging a light beam from said light source upon said photoelectric tube to an extent dependent on the extent of movement of said element; meansfor subjecting said coil to the electrical surge to be integrated; an amplifier controlled by said photo-electric tube and having its output circuit connected to said coil in such-a manner that slight movement of said element due to the surge to be integrated will cause said light beam to swing in a direction to cause said amplifier to act upon said coil so as to return it substantially to its original position; a condenser inchided in the output circuit of said amplifier; and means for measuring the charge stored in said condenser.

6. A magnetic flux meter comprising; a search cell for linking the magnetic field to be measured; a photo-electric tube; a galvanometer including condenser is derived from said amplifier and the it an operating coil, a light source and a mirror .idr projecting light from said light source upon said photo-electric tube to-an extent dependent -on the extent of movement of said operating coil;

a resistance unit; a circuit including said search 'coil, said galvanometer coil and said resistance unit in series; an amplifier controlled by said photo-electric tube and having its output circuit connected across said resistance unit; a condenser connected in series in said output circuit; and means for indicating the charge on said condenser.

7. Electric current surge integrating apparatus comprising; a photo-electric tube; a galvanometer including an operating coil, a light source and a mirror for projecting light from said light source upon said photo-electric tube to an extent dependent on the extent of operation of said coil; an input circuit for said apparatus-including said' coil;- an amplifier controlled by said photo-electric tube and having an output circuit connected to said coil in such manner that operation of said coil due to current flowing in said input circuit will cause the amplifier to produce current in its output circuit and in said coll which substantially neutralizes the current flowing in respon'sive means to thereby charge said condnser by current flow thereinto at a rate proportional to said potential irrespective of the counterpotential existing in said condenser, and

means for measuring the charge on said condenser.

9. A magnetic flux meter comprising; a search coil for linking the magnetic field to be meas ured; a resistance unit; electro-responsive means included in series 'with said resistance unit-and said search coil; an amplifier controlled by said electro-responsive means and having-an output circuit included in series with said resistance unit and so polarized that the potential induced in said search coil will cause said electro-responsive means to control said amplifier to cause current to flow in said output circuit and said resistance unit in series in a direction to produce a voltage drop in said resistance unitwhich opposes and is substantially equal to said induced potential; a condenser included in said-output circuit; and means for indicating the chargeon said condenser.

ROBERT H. DICKE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name a Date 2,012,837 Tear Aug. 27, 1935 2,117,894 Lenehan May 17, 1938 2,136,682 Gilbert Nov. 15, 1938 2,297,543 Eberhardt et al. Sept. 29, 1942 2,364,474 Rich Dec. 5, 1944 2,367,614 Rich Jan. 16, 1945 2,459,730 Williams Jan. 18, 1949 

